Apparatus for detecting the volume of traffic

ABSTRACT

An apparatus for detecting the volume of traffic includes a single oscillator having an oscillating coil which is embedded in the roadbed of a roadway. A converter is provided for converting the output frequency signal of the oscillator to a corresponding voltage signal and a relay device is connected to the output of the converter for responding thereto. The converter is formed so that it will generate an output therefrom only in response to a rapid frequency change in the output of the oscillator.

United States Patent 1 3,688,308

Makoto et al. Aug. 29, 1972 APPARATUS FOR DETECTING THE [56] References Cited VOLUME OF TRAFFIC UNITED STATES PATENTS [72] Inventors: Imamura Makoto, Tokyo; Sato 4 1 41 1 M t al 340 L asak o Japan 3, 5 ,0 6/ 969 aros1e /38 [73] Assignee: Tokyo Shibaura Electric Co., Ltd., Primary ExaminerWilliam C. Cooper Kawasaki-shi, Japan Attorney-Oblon, Fisher and Spivak [22] Filed: Oct. 6, 1970 ABSTRACT 21 Appl. No.: 78,525

An apparatus for detecting the volume of traffic includes a single oscillator having an oscillating coil [30] APPhcatm Pmmy which is embedded in the roadbed of a roadway. A Oct. 6, 1969 Japan ..44/94502 converter is provided for converting the output Nov. 7, 1969 Japan ..44/05037 frequency signal of the oscillator to a corresponding voltage signal and a relay device is connected to the }.LtSCCll. ..340/38 output of the converter for responding thereto The I} o g converter i f d so th t g t an tp t [58] Field of Search ..340/38 L therefrom only in response to a rapid frequency change in the output of the oscillator.

8 Claims, 1 Drawing Figure u u u n ,2? I3 COUNTER [:I] I9 2| 29 2 -ii 2o R E co R o E R l2 8 OSCILLATOR L.

5' Rum/J 1 l9 l4 n v m o l: TELEMETRY i I j ,[lfw DEVICE i l I n 23 i 26 i l l 222 i 25 ELECTRIC VOLTAGE SOURCE APPARATUS FOR DETECTING THE VOLUME OF TRAFFIC BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an apparatus for detecting the volume of traffic and more particularly to a highly accurate apparatus for detecting the volume of traffic for use in traffic control which employs only a single oscillator and is generally immune from external influences.

2. Description of the Prior Art In the past conventional apparatus for detecting the volume of traffic has been generally formed of a first oscillator which functions as a standard and of a second oscillator, having an oscillating coil embedded in the roadbed of a roadway. A mixer was provided for generating a beat or difference signal between the outputs of the two oscillators. The second oscillator was regulated to normally generate a signal of the same frequency as that of the output frequency of the first oscillator when a vehicle was not present over the oscillating coil thereof. Then, when a vehicle would pass over the coil of the second oscillator, the output frequency signal thereof would change and thereby cause the mixer to generate a beat signal which in turn would operate a counting device for enabling a count to be made of the number of vehicles that passed over the coil of the second oscillator.

While somewhat satisfactory, with the prior art apparatus for detecting the volume of trafiic, it was necessary to accurately calibrate both of the oscillators upon the installation thereof in the field. In addition, a problem with the prior art apparatus was that the embedded coil of the second oscillator would often become deformed when a heavy vehicle passed thereover. This would, in turn, vary the constant of the oscillating circuit. Moreover, with the prior art apparatus, the oscillators often would be affected by temperature variations, which again would vary the constants thereof. Additionally, water from rain and the like would often soak into the roadbed and interfere with the oscillating coil of the second oscillator and thereby vary the output frequency thereof.

As a result of the above, inaccuracies in the measurement of the volume of flow of traffic would occur. Furthermore, the prior art apparatus requiring two oscillators was quite expensive, occupied a great deal of space, and requiring accurate calibrations took a long time to install. 1

SUMMARY OF THE INVENTION Accordingly, it is one object of this invention to provide a new and improved unique apparatus for detecting the volume of flow of traffic wherein the need for accurate calibration upon the installation thereof is eliminated.

Another object of this invention is to provide a new and improved unique apparatus for detecting volume of traffic in which any variations in the constant of the oscillator circuit will not affect the operation thereof.

A further object of thisinvention is to provide a new and improved unique apparatus for detecting volume of traffic in which errors resulting from influences due to water soaking into the roadbed of a roadway are effectively eliminated.

One other object of this invention is to provide a new and improved unique apparatus for detecting volume of traffic wherein means are provided for inspecting the stagnation of traffic.

Yet one other object of this invention is to provide a new and improved unique apparatus for detecting volume of traffic which utilizing only a single oscillator is compact, inexpensive, and easy to install.

In accordance with one embodiment of this invention, these and other objects are, in one aspect, attained by the provision of an oscillator having an oscillating coil which is embedded in the roadbed of a roadway. The output frequency of the oscillator is converted into a D.C. voltage proportional to the frequency thereof by the provision of an appropriate converter. This converter is provided with a delay circuit which acts to reduce the output voltage of the converter to a zero level after a predetermined time delay. A relay device is provided which is responsive to the output voltage of the converter for detecting the existence of a vehicle over the oscillating coil of the oscillator.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing, the apparatus for detecting the volume of traffic according to this invention is shown as including a conventional oscillator 10, the frequency of which is determined by a coil 11 which is embedded in the roadbed of a roadway l2, and which forms a portion of the oscillator. When a vehicle, such, for example, as an automobile 13, passes over the coil 12, the same will function as a secondary coil of the coil 11 and thereby reduce the resultant inductance of the oscillating circuit. This will cause the output frequency of the oscillator 10 to suddenly increase.

The output frequency signal of the oscillator 10 is first converted into a current through a converting circuit 14, which includes a capacitor 15 and diodes l6 and 17 connected as shown. The current so developed is then supplied to a conventional operational amplifier 18 which has a feed-back circuit 19 connected in parallel therewith. The feedback circuit 19 includes a resistor 20 and a capacitor 21 which are connected in parallel. The current is thereby converted into a DC. voltage which is proportional to the output frequency of the oscillator 10.

The output voltage of the operational amplifier 18 is then simultaneously supplied to a relay 22, for selectively operating the same, as hereinafter explained, and through a resistor 23 to one terminal of a feed-back amplifier 24. The other input terminal of the feed-back amplifier 24 is grounded. The terminal of the feed-back amplifier 24 to which the resistor 23 is connected is grounded through a capacitor 25 which forms a time delay circuit 26 with the serially connected resistor 23.

In operation, the feed-back amplifier 24 will compare the voltage of the capacitor 25 which is obtained from the time delay circuit 26 with either a zero voltage or the ground voltage level and thereby generate an output signal for reducing the input of the operational amplifier 18 to zero.

From the above description, it can be readily understood that the operational amplifier 18 will generate an output voltage of a sufficient level to cause the relay 22 to operate only when the output frequency of the oscillator 10 makes a sudden change. On the other hand, for slow changes in the output of the oscillator 10, the relay 22 will not operate in that because of the feedback from the amplifier 24, the voltage level applied thereto will not be of a sufficient level for activating the same. It should also be understood that a sudden change in the output of the oscillator 10 will occur when, for example, a vehicle, such as the automobile 13, passes over the embedded coil 11 and that slow changes will occur from such conditions as when water from rain or the like gradually soaks into the roadbed and when the constant of the oscillator circuit varies due to a deformation of the embedded coil, which may occur by successively passing heavy vehicles thereover or from the influence of temperature variations and moisture.

It is now apparent that the relay 22 will respond only to the presence of a vehicle over the oscillating coil 11. Under such conditions, the relay 22 will operate and the contacts 221 and 222 thereof will close. When the contact 221 closes, a conventional counter 27, such as of the digital type, will-receive a pulse from an electrical voltage source (not shown) to thereby register a count for the vehicle whose presence is thereby indicated. When the contact 222 closes, an additional capacitor 28 is connected in parallel with the capacitor 25 such that the time delay of the circuit 26 will increase, and thus the output voltage of the operational amplifier 18 will not be suppressed until after the longer time delay has elapsed.

It should be understood that the provision of a long time delay is very effective in surveying the stagnation of traffic at a particular crossing. Thus, when a stagnation of traffic occurs, a vehicle may be present over the oscillating coil 11 of the oscillator 10 for a long period of time. Though the length of stagnation will depend upon the particular traffic circumstance, it is assumed, for purposes of example, that the longest stagnation time is minutes. With the present invention, this time delay can be easily obtained from the delay circuit 26 with the additional capacitor 28, since the output of the operational amplifier 24 can be held to continue for 5 minutes. On the other hand, if a vehicle passes over the coil 11 within the 5 minute time delay, the output voltage of the operational amplifier 18 will be suppressed in accordance therewith such that the relay 22 will be reset to cause the contacts 221 and 222 to open.

In accordance with the above, the stagnation time of a vehicle can be readily displayed by the provision of a conventional recorder 29 which is energized through the relay contact 221. it should be understood that a conventional telemetry device 30, which is also energized through the relay contact 221, may be provided for transmitting the information on the volume or stagnation of traffic to a remote traffic control room.

It should now be apparent that in accordance with the present invention, it is not necessary for the perforrnance of the apparatus to accurately calibrate the oscillator thereof. This obviously serves to reduce the expense for installation thereof. Moreover, because of the slow variation of the output frequency of the oscillator as a result of water soaking into the roadbed or due to the variation of the constant in the oscillator circuit from the deformation of the embedded coil, as well as from variations of conditions in the environment, the operational amplifier 18 will not generate an output therefrom because of the provision of the feed-back amplifier 24, with the time delay circuit 26, such that any undesirable operation of the relay 22 is eliminated. Moreover, with this invention, by providing the additionalcapacitor 28 across the time delay circuit 26, traffic stagnations can be easily detected.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. Thus, for example, while the present invention has been described with particular reference to antomotive vehicles, it is not so limited but may be similarly employed in controlling the runway of an airport and the like. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

What is claimed is:

I. An apparatus for detecting the volume of traffic which comprises:

an oscillator having an oscillating coil adapted to be embedded in the road bed of a roadway such that the frequency of the output signal of said oscillator will change when a vehicle is present over said coil;

means for converting the frequency of the output signal generated by said oscillator to a voltage proportional thereto;

a time delay circuit coupled to said means for reducing the output of said means to substantially a zero amplitude within a predetermined time delay; and

a relay device connected to the output of said means for responding to the output voltage thereof.

2. An apparatus for detecting the volume of traffic according to claim 1, wherein said time delay circuit is provided with means for changing the constant of the time delay thereof in response to the operation of said relay device.

3. An apparatus for detecting the volume of trafiic according to claim 1, wherein said means includes:

circuit means for receiving the output frequency signal from said oscillator and for producing a corresponding current signal;

an operational amplifier successively connected to said circuit means for converting the output current thereof to a corresponding voltage;

a feed-back amplifier which is provided between the output and the input of the operational amplifier for negatively feeding back the output of the operational amplifier; and

a time-delay circuit which is provided at the output of the operational amplifier, said time delay circuit including a resistor and a first capacitor coupled in series with each other and for supplying a delayed output from the operational amplifier to said feed back amplifier.

4. An apparatus for detecting the volume of traffic according to claim 3, wherein:

a second capacitor is selectively connected in parallel with said first capacitor by said relay device for providing a much longer period of delay whereby the stagnation of trafiic can be determined.

5. An apparatus for detecting the volume of traffic according to claim 1, wherein:

said means is combined with said relay device such that when a vehicle is present over said oscillating coil said relay device is actuated for a predetermined time interval, the relay device releasing as soon as the vehicle passes over the coil within the predetermined time interval.

6. An apparatus for detecting the volume of trafiic according to claim 1, wherein said relay device has an output which is connected to a counter for counting the number of vehicles passing over said oscillating coil. 7. An apparatus for detecting the volume of traffic according to claim 1, wherein I said relay device has an output connected to a recorder for recording any traffic stagnation. 8. An apparatus for detecting the volume of traffic according to claim 1, wherein said relay device has an output connected to a telemetry device for transmitting information on traffic to a remote control room. 

1. An apparatus for detecting the volume of traffic which comprises: an oscillator having an oscillating coil adapted to be embedded in the road bed of a roadway such that the frequency of the output signal of said oscillator will change when a vehicle is present over said coil; means for converting the frequency of the output signal generated by said oscillator to a voltage proportional thereto; a time delay circuit coupled to said means for reducing the output of said means to substantially a zero amplitude within a predetermined time delay; and a relay device connected to the output of said means for responding to the output voltage thereof.
 2. An apparatus for detecting the volume of traffic according to claim 1, wherein said time delay circuit is provided with means for changing the constant of the time delay thereof in response to the operation of said relay device.
 3. An apparatus for detecting the volume of traffic according to claim 1, wherein said means includes: circuit means for receiving the output frequency signal from said oscillator and for producing a corresponding current signal; an operational amplifier successively connected to said circuit means for converting the output current thereof to a corresponding voltage; a feed-back amplifier which is provided between the output and the input of the operational amplifier for negatively feeding back the output of the operational amplifier; and a time-delay circuit which is provided at the output of the operational amplifier, said time delay circuit including a resistor and a first capacitor coupled in series with each other and for supplying a delayed output from the operational amplifier to said feed-back amplifier.
 4. An apparatus for detecting the volume of traffic according to claim 3, wherein: a second capacitor is selectively connected in parallel with said first capacitor by said relay device for providing a much longer period of delay whereby the stagnation of traffic can be determined.
 5. An apparatus for detecting the volume of traffic according to claim 1, wherein: said means is combined with said relay device such that when a vehicle is present over said oscillating coil said relay device is actuated for a predetermined time interval, the relay device releasing as soon as the vehicle passes over the coil within the predetermined time interval.
 6. An apparatus for detecting the volume of traffic according to claim 1, wherein said relay device has an output which is connected to a counter for counting the number of vehicles passing over said oscillating coil.
 7. An apparatus for detecting the volume of traffic according to claim 1, wherein said relay device has an output connected to a recorder for recording any traffic stagnation.
 8. An apparatus for detecting the volume of traffic according to claim 1, wherein said relay device has an output connected to a telemetry device for transmitting information on traffic to a remote control room. 